Quantifying the impact of foliar insects on two Eucalyptus hybrids in Zululand, northern KwaZulu-Natal, South Africa

Abstract

The effects of defoliation by insect pests on Eucalyptus growth in South Africa is poorly understood, with the need for negative impacts to be quantified. In 2010, two long-term insect exclusion trials were established at Palm Ridge and Teza plantations in KwaZulu-Natal to quantify the impact of insect pests on two Eucalyptus hybrids. The trial locations were selected adjacent to compartments in which the pests Gonipterus spp. and Thaumastocoris peregrinus were present. Each trial had an insecticide treatment with an active ingredient of alpha-cypermethrin at a rate of 100 g L⁻¹ and a control treatment where trees were not sprayed. Insect pests were collected after every spraying event with a greater number collected over a period of four months from the Palm Ridge site. Gonipterus spp. were the predominant insect pest collected. No significant growth differences were recorded between treated and untreated trees at Teza. Measurements taken at Palm Ridge indicated that insecticide-treated trees had significantly better tree growth than untreated trees. Final measurements showed a 25% reduction in volume for the control treatment compared with the insecticide treatment. Results of this study indicate that timing and duration of insecticide application could hold larger and additive benefits for insect exclusion.